Support EventStore Projection

For EventStore storage specifically, it looks like this library is designed so that EventStore is only used for storage of events and that subsequent communicating that events occured is offloaded to Kafka. The EventStore product does support messaging via PersistentSubscription and it would be nice for smaller projects to be able to use just EventStore and not have to spin up a Kafka cluster if that kind of scale is not needed.

Specifically I'd love an API where you can subscribe either to a specific aggregate `user-1234` or a projection `user-*` and have the library handle things like checkpointing (storing the last read offset for a client in EventStore itself) similar to how PersistentSubscriptions work in the EventStore API today.